Embryology: Early Embryonic Development

Question 0

30hr, 40hr, 72hr post fertilization

Answer 0

30hr: 2 cells stage
40hr: 4 Cell stage
72 hour (3 days): 12-16 cell stage

Question 1

Site of fertilization

Answer 1

Ampullary region of Fallopian tube

Question 2

Compaction

Answer 2

After 8 cell stage cells have made maximum contact with each other
Separate into inner and outer cells

Question 3

Morula

Answer 3

16 cell stage
Inner cells: Inner cell mass (embryo)
Outer cells: outer cell mass (trophoblast–>placenta)

Question 4

When morula migrates into uterus, it enlarges and becomes the _____

Answer 4

Blastocyst

Question 5

Fluid penetrates inner cell mass and forms this single cavity

Answer 5

Blastocele

Question 6

3 parts of blastocyst

Answer 6

Trophoblast: outer covering formed from outer cell mass, eventually become epithelial wall
Blastocele
Embryoblast: inner cell mass located at one pole

Question 7

Day 6

Answer 7

Implantation:

• trophoblast cells penetrate uterine wall
• oriented so inner cell mass near endometrium

Question 8

Day 8

Answer 8

Blastocyst partially embedded

Trophoblast differentiates into Cytotrophoblast and syncytiotrophoblast

Question 9

Inner cell mass differentiates into:

Answer 9

Hypoblast layer (entoderm)
Epiblast layer (ectoderm)

Question 10

Day 11-12

Answer 10

Completely embedded

Beginning of uteroplacental circulation

Question 11

Cytotrophoblast becomes:

Answer 11

Amnion

Amniotic cavity

Question 12

When does gastrulation begin?

Answer 12

Day 8

Question 13

How does gastrulation begin?

Answer 13

Formation of primitive streak

Cells of Epiblast migrate to primitive streak, then slip below it

Question 14

Source of the germ layers

Answer 14

Epiblast

Question 15

Layer of inner cell mass bordering amniotic sac

Answer 15

Epiblast

Question 16

Layer of inner cell mass bordering blastocele (yolk sac)

Answer 16

Endoderm

Question 17

Ectoderm becomes:

Answer 17

Skin
Teeth
Mouth glands
Nervous system
Some endocrine glands

Question 18

Endoderm becomes:

Answer 18

Epithelium of digestive tract, respiratory system, bladder, vagina, urethra

Question 19

Mesoderm becomes:

Answer 19

All connective tissue, muscular, skeletal, lymphatic, and circulatory systems

Question 20

When does cardiovascular system appear?

Answer 20

Middle of the 3rd week

Question 21

First system to reach a functional state

Answer 21

Cardiovascular system

Question 22

Day 16-18

Answer 22

Progenitor heart cells at cranial end of primitive streak move through streak into splanchnic layer
Primitive heart field forms

Question 23

2 things progenitor heart cells create:

Answer 23

Cardiac myocytes and blood islands

Question 24

Formation of intraembryonic coelom:

Answer 24

Joining of small spaces in lateral mesoderm
Extend cranially and fuse to form horseshoe shaped cavity
Eventually become pericardial cavity